Two-Stage Piston Rocket

I've made a two-stage rocket that uses gap staging, and I've made a high-power two-stage rocket that uses electronics to ignite the upper-stage. This project creates something more complicated but even more efficient. This rocket still electronically ignites the upper stage, but it gives the upper stage more speed and power when seperating from the lower stage by adding a piston inside the rocket. Here's how it works:

• Unlike my other electronically ignited two-stage rocket, the electronics bay, which holds the flight computer and battery, is in the first stage. After a predetermined time after launch, the electronics ignite the upper stage motor.

• The piston is also in the first stage. When the upper-stage motor ignites, its exhaust gases build pressure under the piston, pushing it up. The upper-stage is temporarily attached to the piston, so the piston accelerates the upper-stage, until the piston reaches its maximum extension, at which point the upper-stage flies off. This reuse of the upper-stage motor's exhaust gases makes the rocket faster and more efficient.